Method for manufacturing negative electrode, negative electrode, and secondary battery including the same

Abstract

The present invention relates to a method for producing a negative electrode, a negative electrode, and a secondary battery including the same.

Description

Technical Field

[0001] This application claims the benefit of the filing date of Korean Patent Application No. 10-2021-0148034, filed with the Korean Intellectual Property Office on November 1, 2021, and all of its contents are incorporated herein by reference.

[0002] The present invention relates to a method for manufacturing a negative electrode, a negative electrode, and a secondary battery including the same.

Background Art

[0003] In recent years, with the rapid spread of electronic devices using batteries, such as mobile phones, notebook computers, and electric vehicles, the demand for small and lightweight secondary batteries with relatively high capacities has been increasing rapidly. In particular, lithium secondary batteries are lightweight and have a high energy density, and have been in the spotlight as a driving power source for portable devices. Accordingly, research and development efforts for improving the performance of lithium secondary batteries have been actively underway.

[0004] Generally, a lithium secondary battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, an electrolyte, an organic solvent, and the like. Further, on the current collector, an active material layer including a positive electrode active material and a negative electrode active material can be formed on the positive electrode and the negative electrode, respectively. Generally, lithium-containing metal oxides such as LiCoO2 and LiMn2O4 are used as the positive electrode active material for the positive electrode, and carbon-based active materials and silicon-based active materials that do not contain lithium are used as the negative electrode active material for the negative electrode.

[0005] Among the negative electrode active materials, in the case of silicon-based active materials, they are noted for having a higher capacity than carbon-based active materials and excellent fast charging characteristics. However, silicon-based active materials have disadvantages in that the degree of volume expansion / contraction during charge and discharge is large and the irreversible capacity is large, resulting in low initial efficiency.

[0006] On the other hand, among silicon-based active materials, silicon-based oxides, specifically SiO xIn the case of silicon-based oxides represented by (0 < x < 2), there is an advantage in that the degree of volume expansion / contraction due to charge and discharge is lower compared to other silicon-based active materials such as silicon (Si). However, there is still a drawback that the initial efficiency decreases due to the presence of irreversible capacity in silicon-based oxides.

[0007] Regarding this, research has been continuously conducted to reduce the irreversible capacity and improve the initial efficiency by doping or inserting metals such as Li, Al, and Mg into silicon-based oxides. However, in the case of a negative electrode slurry containing a metal-doped silicon-based oxide as a negative electrode active material, there is a problem that the metal oxide formed by doping reacts with moisture to increase the pH of the negative electrode slurry and change the viscosity, resulting in a poor state of the manufactured negative electrode and a problem of reduced charge and discharge efficiency of the negative electrode.

[0008] Therefore, there is a current need to develop a method capable of improving the phase stability of a negative electrode slurry containing a silicon-based oxide and improving the charge and discharge efficiency and lifespan of the negative electrode manufactured therefrom.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0010] The present invention relates to a method for manufacturing a negative electrode, a negative electrode, and a secondary battery including the same.

Means for Solving the Problems

[0011] One embodiment of the present invention provides a method for manufacturing a negative electrode, comprising the steps of: preparing a preliminary negative electrode slurry containing a negative electrode active material including silicon-based particles containing a Li compound and a conductive material; adding an acid to the preliminary negative electrode slurry and mixing to form a negative electrode slurry; applying the negative electrode slurry to at least one surface of a current collector, drying and rolling for the first time to form a negative electrode active material layer; and drying the current collector with the negative electrode active material layer formed thereon for the second time, wherein the pH of the negative electrode slurry at 25°C is 10 or more and less than 12.5.

[0012] One embodiment of the present invention provides a negative electrode manufactured by the above manufacturing method.

[0013] One embodiment of the present invention provides a negative electrode including a current collector and a negative electrode active material layer provided on the current collector, wherein the negative electrode active material layer contains a negative electrode active material, the negative electrode active material contains silicon-based particles containing a Li compound, and after separating the negative electrode active material layer from the current collector, the pH of a dispersion obtained by mixing 5 g of the negative electrode active material layer and 100 g of water is 10 or more and less than 12.5 at 25°C.

[0014] One embodiment of the present invention provides a secondary battery including the above negative electrode.

Advantages of the Invention

[0015] The manufacturing method of the present invention can suppress side reactions of the negative electrode slurry by adding an acid, has the effect of lowering the pH of the slurry and improving the phase stability of the slurry. In addition, the lithium silicate gel generated by adding an acid can increase the porosity around the negative electrode active material during electrode manufacturing. Therefore, the space around the negative electrode active material in the electrode can be ensured, deformation of the electrode due to volume expansion of the negative electrode active material is minimized, and the life of the electrode is improved.

[0016] In the case of a negative electrode using silicon-based particles containing a conventional Li compound, during the production of an aqueous slurry, the slurry shows basicity due to lithium by-products, and the dispersion liquid in which the negative electrode active material layer is dispersed shows a high pH. On the other hand, for the negative electrode according to the present invention, although it contains silicon-based particles containing a Li compound, the dispersion liquid in which the negative electrode active material layer is dispersed has a relatively low pH. Therefore, a battery using the negative electrode can show significantly improved charge-discharge capacity, initial efficiency, and lifespan.

Mode for Carrying Out the Invention

[0017] Hereinafter, the present specification will be described in more detail.

[0018] In this specification, when a certain part says that it "includes" a certain component, this means that, unless otherwise stated to the contrary, it does not exclude other components, but may further include other components.

[0019] In this specification, when it is said that a certain member is located "on" another member, this includes not only the case where a certain member is in contact with another member, but also the case where another member exists between the two members.

[0020] The terms or words used in this specification should not be construed as being limited to their ordinary or dictionary meanings. Based on the principle that the inventor can appropriately define the concept of the terms in order to explain his invention in the best way, they should be construed in a meaning and concept consistent with the technical idea of the present invention.

[0021] The singular expressions of the terms used in this specification include plural expressions unless the context clearly indicates otherwise.

[0022] In this specification, the presence and content of elements in the negative electrode active material can be confirmed by ICP analysis, and the ICP analysis can be performed using an inductively coupled plasma optical emission spectrometry (ICPAES, Perkin-Elmer 7300).

[0023] In this specification, the average particle size (D 50 ) can be defined as the particle size corresponding to 50% of the volume cumulative amount in the particle size distribution curve (graph curve of the particle size distribution degree) of the particles. The average particle size (D 50 ) can be measured, for example, using the laser diffraction method. The laser diffraction method can generally measure particle sizes in the range from the submicron region to about several millimeters, and can obtain highly reproducible and highly resolvable results.

[0024] In this specification, the BET specific surface area can be measured by using a BET measuring apparatus (BEL-SORP-MAX, Nippon Bell) for the measurement target, removing gas (degassing) at 130°C for 5 hours, and allowing N2 adsorption / desorption to proceed at 77K and measuring by the BET six-point method.

[0025] Hereinafter, preferred embodiments of the present invention will be described in detail. However, the embodiments of the present invention can be changed into various forms, and the scope of the present invention is not limited to the embodiments described below.

[0026] One embodiment of the present invention includes a step (S1) of preparing a preliminary negative electrode slurry containing a negative electrode active material and a conductive material, the negative electrode active material containing silicon-based particles containing an Li compound; a step (S2) of adding an acid to the preliminary negative electrode slurry and mixing to form a negative electrode slurry; a step (S3) of applying the negative electrode slurry to at least one surface of a current collector, drying and rolling for the first time to form a negative electrode active material layer; and a step (S4) of drying the current collector on which the negative electrode active material layer is formed for the second time, and provides a method for manufacturing a negative electrode, wherein the pH of the negative electrode slurry at 25°C is 10 or more and less than 12.5.

[0027] Generally, when doping a silicon-based oxide with Li, there is an advantage that the initial efficiency increases. However, due to lithium by-products that are not reacted with the silicon-based oxide, the aqueous slurry becomes basic during production, and the Si of the negative electrode active material reacts with the base (OH -) reacts to generate gas, resulting in a problem that the rheological properties change.

[0028] To solve this problem, an acid is added during the process of mixing the slurry to neutralize the base in the slurry, thereby suppressing the reaction between the base (OH - ) and Si. In addition, when the acid is added, the acid reacts with lithium silicate to form a lithium silicate gel. Therefore, when the negative electrode slurry is coated on the current collector and dried, and after rolling, the water adsorbed on the lithium silicate gel evaporates at the stage of final drying of the electrode, inducing volume shrinkage of the gel. As a result, voids can be increased around the negative electrode active material, space around the negative electrode active material is ensured, and deformation of the electrode due to volume expansion of the negative electrode active material is minimized, thus having the effect of improving the lifespan.

[0029] In addition, the generated lithium silicate gel shrinks and coats the periphery of the silicon-based particles, and the lithium silicate gel coating layer can act as a resistor to prevent Li elution from the silicon-based particles.

[0030] The method for manufacturing a negative electrode according to an embodiment of the present invention includes a step (S1) of preparing a preliminary negative electrode slurry including a negative electrode active material including silicon-based particles containing a Li compound and a conductive material.

[0031] In an embodiment of the present invention, the negative electrode active material may include silicon-based particles containing SiO x (0 < x < 2) and a Li compound.

[0032] The SiO x (0 < x < 2) corresponds to a matrix in the silicon-based particles. The SiO x (0 < x < 2) may be in a form containing Si and SiO2, and the Si may form a phase. That is, the x corresponds to the number ratio of O to Si contained in the SiO x (0 < x < 2). When the silicon-based particles are the SiO x(0 < x < 2) is included, the discharge capacity of the secondary battery can be improved.

[0033] The silicon-based particles contain a Li compound. The Li compound can exist in at least one form of lithium atom, lithium silicate, lithium silicide, and lithium oxide within the silicon-based particles, and preferably can exist in the form of lithium silicate. When the silicon-based particles contain a Li compound, there is an effect of improving the initial efficiency.

[0034] The Li compound may be included in the silicon-based particles through a step of heating and vaporizing a mixed powder of Si and SiO2, depositing the vaporized mixed gas to form SiO, mixing the formed SiO with Li powder, and then performing heat treatment.

[0035] That is, the Li compound can be distributed on the surface and / or inside of the silicon-based particles in a form doped into the silicon-based particles. The Li compound is distributed on the surface and / or inside of the silicon-based particles, can control the volume expansion / contraction of the silicon-based particles to an appropriate level, and can play a role in preventing damage to the active material. Also, the Li compound may be included in terms of reducing the ratio of the irreversible phase (e.g., SiO2) of the silicon-based oxide particles to improve the efficiency of the active material.

[0036] The Li compound may be lithium silicate, and the lithium silicate is Li a Si b O c represented by (2 ≤ a ≤ 4, 0 < b ≤ 2, 2 ≤ c ≤ 5), and can exist in the form of at least one lithium silicate selected from the group consisting of Li2SiO3, Li4SiO4, and Li2Si2O5 within the silicon-based particles.

[0037] In one embodiment of the present invention, the Li may be contained in an amount of 1 to 20 parts by weight, 4 to 12 parts by weight, or 5 to 10 parts by weight based on 100 parts by weight of the total negative electrode active material. Specifically, it may be contained in an amount of 6 to 9 parts by weight, and more specifically, it may be contained in an amount of 7 to 8 parts by weight. As the content of Li increases, the initial efficiency increases, but there is a problem that the discharge capacity decreases. Therefore, when the above range is satisfied, appropriate discharge capacity and initial efficiency can be realized.

[0038] The content of the Li element can be confirmed by ICP analysis. Specifically, after collecting a certain amount (about 0.01 g) of the negative electrode active material, it is transferred to a platinum crucible, nitric acid, hydrofluoric acid, and sulfuric acid are added, and it is completely decomposed on a hot plate. Then, using an inductively coupled plasma atomic emission spectrometer (ICPAES, Perkin-Elmer 7300), the intensity of a standard solution (5 mg / kg) prepared using the characteristic wavelength of the element to be analyzed is measured to create a reference calibration curve. After that, the pretreated sample solution and the background sample are introduced into the instrument, the intensities of each are measured to calculate the actual intensity, the concentration of each component is calculated by comparing with the calibration curve created above, and then the element content of the manufactured negative electrode active material is analyzed by converting so that the total sum becomes the theoretical value.

[0039] In one embodiment of the present invention, a carbon layer may be provided on at least a part of the surface of the silicon-based particles. At this time, the carbon layer may be partially coated on at least a part of the surface, that is, the particle surface, or may be in a form covering the entire particle surface. The carbon layer imparts conductivity to the negative electrode active material, and the initial efficiency, life characteristics, and battery capacity characteristics of the secondary battery can be improved.

[0040] Specifically, the carbon layer may contain crystalline carbon or amorphous carbon, and preferably may contain amorphous carbon.

[0041] The crystalline carbon can further improve the conductivity of the negative electrode active material. The crystalline carbon may include at least one selected from the group consisting of fullerene, carbon nanotube, and graphene.

[0042] The amorphous carbon can appropriately maintain the strength of the carbon layer and suppress the expansion of the silicon-based particles. The amorphous carbon may be at least one carbide selected from the group consisting of tar, pitch, and other organic substances, or a carbon-based substance formed by using a hydrocarbon as a source in a chemical vapor deposition method.

[0043] The carbide of the other organic substance may be a carbide of an organic substance selected from the group consisting of sucrose, glucose, galactose, fructose, lactose, mannose, ribose, aldose or ketose, and combinations thereof.

[0044] The hydrocarbon can be a substituted or unsubstituted aliphatic or alicyclic hydrocarbon, or a substituted or unsubstituted aromatic hydrocarbon. The aliphatic or alicyclic hydrocarbon of the substituted or unsubstituted aliphatic or alicyclic hydrocarbon may be methane, ethane, ethylene, acetylene, propane, butane, butene, pentane, isobutane, or hexane, etc. The aromatic hydrocarbon of the substituted or unsubstituted aromatic hydrocarbon includes benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, indene, coumarone, pyridine, anthracene, or phenanthrene, etc.

[0045] Specifically, the carbon layer can be formed by placing a carbonaceous precursor on the silicon-based particles and then performing heat treatment. The carbonaceous precursor may be graphene, graphite, etc. for the production of crystalline carbon, or at least one carbide selected from the group consisting of tar, pitch, and other organic substances for the production of amorphous carbon, or a carbon-based substance formed by using a hydrocarbon such as methane, ethane, acetylene, etc. as a source in a chemical vapor deposition method.

[0046] The average particle size (D 50 ) of the negative electrode active material is from 0.1 μm to 30 μm, specifically from 1 μm to 20 μm, and more specifically may be from 1 μm to 10 μm. When the above range is satisfied, the structural stability of the active material during charge and discharge can be achieved, and problems such as an increase in the volume expansion / shrinkage level as the particle size becomes excessively large can be prevented, and problems such as a decrease in the initial efficiency due to an excessively low particle size can be prevented.

[0047] The particle size of the negative electrode active material can be adjusted by methods such as a ball mill, a jet mill, or air classification, and is not limited thereto.

[0048] In one embodiment of the present invention, the preliminary negative electrode slurry contains the negative electrode active material and a conductive material.

[0049] The preliminary negative electrode slurry may further contain an additional negative electrode active material.

[0050] As the additional negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium can be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, and Al alloys; SiO β (0 < β < 2), SnO 2、Metal oxides capable of doping and undoping lithium, such as vanadium oxide, lithium titanium oxide, lithium vanadium oxide; or composites containing the metallic compound and the carbonaceous material, such as Si-C composites or Sn-C composites, etc. may be mentioned, and any one or a mixture of two or more of these may be used. Further, a thin film of metallic lithium may be used as the negative electrode active material. Also, as the carbon material, any of low-crystalline carbon and highly crystalline carbon may be used. Representative examples of low-crystalline carbon are soft carbon and hard carbon, and representative examples of highly crystalline carbon are amorphous, plate-like, flaky, spherical or fibrous natural graphite or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch derived cokes.

[0051] The additional negative electrode active material may be a carbon-based negative electrode active material.

[0052] In one embodiment of the present invention, the weight ratio of the negative electrode active material and the additional negative electrode active material contained in the preliminary negative electrode slurry is 10:90 to 90:10, and specifically may be 10:90 to 50:50.

[0053] In one embodiment of the present invention, the preliminary negative electrode slurry may further contain a thickener. The thickener may be carboxymethyl cellulose (CMC), but is not limited thereto, and thickeners used in this technical field can be appropriately employed.

[0054] In one embodiment of the present invention, the preliminary negative electrode slurry may further contain a binder. The binder may include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, poly acrylic acid, and substances in which their hydrogens are substituted with Li, Na, Ca, etc., and may also include various copolymers thereof.

[0055] In one embodiment of the present invention, the conductive material is not particularly limited as long as it has conductivity without inducing a chemical change in the battery. For example, graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon, aluminum, nickel powder; conductive whiskers such as zinc oxide, potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives can be used.

[0056] In one embodiment of the present invention, the negative electrode active material may be contained in the preliminary negative electrode slurry in an amount of 60 to 99 parts by weight, specifically 70 to 98 parts by weight, based on 100 parts by weight of the solid content of the preliminary negative electrode slurry.

[0057] In one embodiment of the present invention, the conductive material may be included in the preliminary negative electrode slurry in an amount of 0.5 to 25 parts by weight, specifically 0.5 to 20 parts by weight, more specifically 1 to 20 parts by weight, 1 to 10 parts by weight, or 1 to 5 parts by weight based on 100 parts by weight of the total solid content of the preliminary negative electrode slurry.

[0058] In one embodiment of the present invention, the thickening agent may be included in the preliminary negative electrode slurry in an amount of 0.5 to 25 parts by weight, specifically 0.5 to 20 parts by weight, more specifically 1 to 20 parts by weight based on 100 parts by weight of the total solid content of the preliminary negative electrode slurry.

[0059] In one embodiment of the present invention, the binder may be included in the preliminary negative electrode slurry in an amount of 0.5 to 30 parts by weight, specifically 0.5 to 20 parts by weight, more specifically 1 to 20 parts by weight based on 100 parts by weight of the total solid content of the preliminary negative electrode slurry.

[0060] The preliminary negative electrode slurry according to one embodiment of the present invention may further include a solvent for forming a negative electrode slurry. Specifically, the solvent for forming a negative electrode slurry may be at least one selected from the group consisting of distilled water, ethanol, methanol, and isopropyl alcohol, specifically, it may include distilled water, in terms of facilitating the dispersion of components.

[0061] In one embodiment of the present invention, the solid content weight of the preliminary negative electrode slurry may be 20 to 75 parts by weight, specifically 30 to 70 parts by weight based on 100 parts by weight of the total preliminary negative electrode slurry.

[0062] The viscosity of the preliminary negative electrode slurry at 25°C may be 3000 cP to 6000 cP, specifically 4000 cP to 6000 cP.

[0063] On the surface of the negative electrode active material contained in the preliminary negative electrode slurry, lithium silicate eluted from the negative electrode active material is present. Further, in the preliminary negative electrode slurry, there are lithium by-products generated by unreacted lithium that was not doped during the production of the negative electrode active material. Specifically, the lithium by-product may be at least one selected from the group consisting of Li2O, LiOH, and Li2CO3.

[0064] The preliminary negative electrode slurry will have basicity due to lithium silicate and lithium by-products.

[0065] The pH of the preliminary negative electrode slurry at 25 °C may be 12.5 or more. Specifically, it may be 12.5 or more and 13 or less, or it may be 12.5 or more and 12.8 or less. More specifically, it may be 12.5 or more and 12.6 or less, or it may be 12.5.

[0066] The method for manufacturing a negative electrode according to an embodiment of the present invention includes a step (S2) of adding an acid to the preliminary negative electrode slurry and mixing to form a negative electrode slurry.

[0067] In one embodiment of the present invention, the pH of the negative electrode slurry at 25 °C is 10 or more and less than 12.5.

[0068] In one embodiment of the present invention, the negative electrode slurry contains lithium silicate gel (Li-silicate Gel).

[0069] When performing X-ray diffraction (XRD) analysis of the negative electrode slurry, a peak may appear at 2θ = 23.2 ± 0.5°. Specifically, a peak may appear around 2θ = 23.2°. The peak is due to the lithium silicate gel.

[0070] In this specification, the X-ray diffraction analysis can be measured using an X-ray diffraction (XRD) instrument (product name: D4-endavor, manufacturer: bruker).

[0071] In this specification, "gel" means a form in which a sol solidifies by forming a network structure of chemical bonds. Specifically, lithium silicate gel is a kind of hydrogel and is produced by the reaction of lithium silicate and an acid. For example, it may be a network structure in which silicon and oxygen are connected in a network and lithium is bonded therein.

[0072] The base contained in the preliminary negative electrode slurry has a problem that it reacts with Si present in the negative electrode active material to generate gas and changes the rheological properties of the slurry. Therefore, by adding and mixing an acid to the preliminary negative electrode slurry, the base (OH - ) present in the preliminary negative electrode slurry can be neutralized to suppress the reaction between Si contained in the negative electrode active material and the base.

[0073] Also, lithium silicate eluted from the negative electrode active material containing a Li compound will be present around the negative electrode active material. However, the added acid promotes the gel formation of lithium silicate, and the negative electrode active material will exist in a form in which a lithium silicate gel is formed around it. After that, since the water adsorbed on the lithium silicate gel evaporates during the drying process of the rolled electrode, the porosity around the negative electrode active material can be selectively increased. Therefore, there is an advantage that the deformation of the electrode due to the volume expansion of the negative electrode active material during charge and discharge of the battery can be minimized and the life can be improved.

[0074] In one embodiment of the present invention, the acid may be at least one selected from the group consisting of phosphoric acid, acetic acid, citric acid, oxalic acid, and boric acid. When using the acid, since the acidity is not high, there is an effect of not impairing the chemical properties such as thickeners and binders when added to the slurry.

[0075] In one embodiment of the present invention, the pK of the acid at 25 °Ca is from 1 to 15, and specifically may be from 1.5 to 13 。 said pK a By using an acid that satisfies the range, there is an effect of not impairing the chemical properties such as the thickener and the binder when added to the slurry. On the other hand, when a strong acid that does not satisfy the range is used, chemical damage to the thickener and the binder occurs, excessive gelation occurs, and the slurry viscosity also rises excessively, resulting in a problem of deteriorating the coating quality of the electrode.

[0076] In one embodiment of the present invention, the acid can be added in an amount of 0.01 part by weight to 1.5 parts by weight based on 100 parts by weight in total of the preliminary negative electrode slurry. Specifically, it may be added in an amount of 0.1 part by weight to 1 part by weight, or may be added in an amount of 0.1 part by weight to 0.8 part by weight. More specifically, it may be added in an amount of 0.4 part by weight to 0.8 part by weight, or may be added in an amount of 0.4 part by weight to 0.6 part by weight. When the content of the acid satisfies the above range, there is an effect of causing gelation to an appropriate degree. On the other hand, when the content of the acid exceeds the above range, chemical damage to the thickener and the binder occurs, excessive gelation occurs, and the slurry viscosity also rises excessively, resulting in a problem of deteriorating the coating quality of the electrode.

[0077] Specifically, the lower limit of the content of the acid is 0.01 part by weight, 0.1 part by weight, 0.2 part by weight, 0.3 part by weight, 0.4 part by weight or 0.5 part by weight, and the upper limit may be 1.5 parts by weight, 1.4 parts by weight, 1.3 parts by weight, 1.2 parts by weight, 1.1 parts by weight, 1 part by weight, 0.9 part by weight, 0.8 part by weight, 0.7 part by weight or 0.6 part by weight.

[0078] In one embodiment of the present invention, in the process of mixing the slurry, a method known in the art can be appropriately adopted.

[0079] In one embodiment of the present invention, the step of adding an acid to the preliminary negative electrode slurry and mixing to form a negative electrode slurry further includes the step of adding a binder and mixing after adding and mixing the acid to the preliminary negative electrode slurry.

[0080] The binder may include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, poly acrylic acid, and substances in which their hydrogens are substituted with Li, Na, Ca, etc., and may also include various copolymers thereof.

[0081] In one embodiment of the present invention, the binder may be included in the negative electrode slurry in an amount of 0.5 to 30 parts by weight, specifically 1 to 20 parts by weight, more specifically 1 to 5 parts by weight, based on 100 parts by weight of the negative electrode slurry.

[0082] In one embodiment of the present invention, the pH of the negative electrode slurry at 25°C may be 10 or more and less than 12.5. Specifically, it may be more than 10 and 12 or less, or 10.5 or more and less than 12, and more specifically 11 or more and 11.5 or less. By the pH of the negative electrode slurry satisfying the above range, an appropriate amount of gelation occurs, and the generated gel has the effect of serving as a buffer against volume expansion in the electrode. On the other hand, when the pH of the negative electrode slurry is less than 10, there is a problem that the coating uniformity of the electrode decreases due to excessive gelation, and when the pH of the negative electrode slurry exceeds 12.5, there is a problem that gas generation is accelerated in the slurry state.

[0083] The lower limit of the pH of the negative electrode slurry may be 10, 10.5, 10.6, 10.7, 10.8 or 10.9, and the upper limit may be 12.4, 12, 11.9, 11.8, 11.7, 11.6 or 11.5.

[0084] In one embodiment of the present invention, the viscosity of the negative electrode slurry at 25 °C may be 6000 cP to 20000 cP, specifically 8000 cP to 15000 cP.

[0085] When the viscosity of the negative electrode slurry is within the above range, the coating property of the negative electrode slurry is improved, and a negative electrode with excellent quality can be realized. At this time, the viscosity can be measured using a viscometer (equipment name: HR20, manufacturer: TA) at 25 °C.

[0086] The method for manufacturing a negative electrode according to one embodiment of the present specification includes a step (S3) of applying the negative electrode slurry to at least one surface of a current collector, and performing first drying and rolling to form a negative electrode active material layer.

[0087] The current collector is a negative electrode current collector, and it is not particularly limited as long as it does not induce a chemical change in the battery and has conductivity. For example, as the current collector, copper, stainless steel, aluminum, nickel, titanium, fired carbon, or a material obtained by surface treatment with carbon, nickel, titanium, silver, etc. on the surface of aluminum or stainless steel may be used. Specifically, a transition metal that adsorbs carbon well, such as copper or nickel, can be used as the current collector. The thickness of the current collector may be 6 μm to 20 μm, but the thickness of the current collector is not limited thereto.

[0088] The method for applying the negative electrode slurry is not particularly limited as long as it is a method commonly used in the art. For example, a coating method using a slot die may be used, and in addition, a Meyer bar coating method, a gravure coating method, a dipping coating method, a spray coating method, etc. may be used.

[0089] The first drying of the negative electrode slurry may be performed at 80°C to 110°C for 3 minutes to 1 hour.

[0090] Specifically, the first drying can be performed in a chamber where hot air circulates for 3 minutes to 1 hour, 3 minutes to 30 minutes, or 3 minutes to 10 minutes. More specifically, it may be performed for 5 minutes. When the above range is satisfied, it has the effect of removing the moisture excluding the water inside the gel.

[0091] Specifically, the first drying can be performed at 80°C to 110°C, preferably 90°C to 100°C. When the above range is satisfied, it has the effect of removing the moisture excluding the water inside the gel.

[0092] During the first drying, the main moisture (free water) contained in the current collector coated with the negative electrode slurry evaporates, but the moisture adsorbed on the lithium silicate gel does not evaporate.

[0093] In addition, the lithium silicate gel shrinks and firmly coats the periphery of the negative electrode active material, and the lithium silicate gel coating layer can act as a resistor to prevent the elution of Li from the negative electrode active material.

[0094] The rolling step can be appropriately performed by adopting a method commonly used in the art.

[0095] At this time, the packing density may be 1 g / cc to 2 g / cc, but is not limited thereto.

[0096] The method for manufacturing a negative electrode according to an embodiment of the present specification includes a step (S4) of second-drying the current collector on which the negative electrode active material layer is formed.

[0097] The second drying of the current collector may be performed at 80°C to 130°C for 6 hours to 10 hours. When the above range is satisfied, it has the effect of removing the remaining water inside the gel.

[0098] Specifically, the second drying can be carried out under the condition of 8 hours using a vacuum chamber. When the above range is satisfied, it has the effect of removing the remaining water inside the gel.

[0099] Specifically, the second drying can be carried out at 80°C to 130°C, preferably 100°C to 130°C. When the above range is satisfied, it has the effect of removing the remaining water inside the gel.

[0100] During the second drying, the moisture of the lithium silicate gel located around the negative electrode active material contained in the negative electrode active material layer will evaporate, and the porosity around the negative electrode active material can be increased in this process. The formed voids play a role in minimizing the deformation of the negative electrode due to the volume expansion of the negative electrode active material during charge and discharge of the battery and improving the service life.

[0101] The BET specific surface area of the negative electrode after the second drying is 2 m 2 / g to 5 m 2 / g. Specifically, it is 2 m 2 / g to 4 m 2 / g. More specifically, it is 2 m 2 / g to 3 m 2 / g. Even more specifically, it may be 2.5 m 2 / g to 3 m 2 / g.

[0102] The BET specific surface area of the negative electrode after the second drying can increase by 5% to 40% compared to the BET specific surface area of the negative electrode before the second drying (the current collector on which the negative electrode active material layer is formed). Specifically, it can increase by 10% to 40%, 15% to 38%, 18% to 35%, or 20% to 35%.

[0103] The negative electrode manufactured by the manufacturing method according to the present invention can provide a larger specific surface area than the conventional negative electrode because voids are formed by gelation due to acid addition. Further, in the case of a conventional negative electrode, since a lithium silicate gel is not formed, there is almost no change in the specific surface area of the negative electrode due to the second drying. However, the negative electrode according to the present invention can evaporate the moisture adsorbed on the lithium silicate gel in the negative electrode active material layer through the second drying to increase the porosity around the negative electrode active material, and has the advantage of minimizing the deformation of the negative electrode due to the volume expansion of the negative electrode active material during charge and discharge of the battery.

[0104] One embodiment of the present invention provides a negative electrode manufactured by the manufacturing method. The negative electrode manufactured as described above may include a structure in which voids are formed around the negative electrode active material.

[0105] Specifically, the BET specific surface area of the negative electrode is 2 m 2 / g to 5 m 2 / g, specifically 2 m 2 / g to 4 m 2 / g, more specifically 2 m 2 / g to 3 m 2 / g, more specifically 2.5 m 2 / g to 3 m 2 / g, and may be 2.5 m 2 / g to 3 m

[0106] One embodiment of the present invention is a negative electrode including a current collector; and a negative electrode active material layer provided on the current collector, the negative electrode active material layer including a negative electrode active material, the negative electrode active material including silicon-based particles containing an Li compound, and after separating the negative electrode active material layer from the current collector, providing a negative electrode in which the pH of a dispersion obtained by mixing 5 g of the negative electrode active material layer and 100 g of water is 10 or more and less than 12.5 at 25°C.

[0107] The pH of the negative electrode dispersion may be 10 or more and less than 12, 10.5 or more and 12 or less, 10.7 or more and 11.7 or less, or 10.8 or more and 11.6 or less at 25°C.

[0108] When the conventional negative electrode contains a negative electrode active material including silicon-based particles containing a Li compound, when the negative electrode active material layer containing the negative electrode active material is separated and mixed with water, it will show a very high pH. On the other hand, even when the negative electrode of the present invention uses silicon-based particles containing a Li compound as the negative electrode active material, after separating the negative electrode from the current collector and mixing it with water to measure the pH, it shows a lower pH than before, and can show the results of significantly improved charge-discharge capacity, initial efficiency, and life.

[0109] In one embodiment of the present invention, the packing density of the negative electrode is 1 g / cc to 2 g / cc, and the BET specific surface area of the negative electrode is 2 m 2 / g to 5 m 2 / g may also be acceptable.

[0110] When the conventional negative electrode contains a negative electrode active material including silicon-based particles containing a Li compound, when the specific surface area of the negative electrode is less than 2 m 2 / g, it becomes impossible to accommodate the volume change of the negative electrode active material, and there is a problem of being vulnerable to electrode deformation. On the other hand, the negative electrode of the present invention has a BET specific surface area of 2 m 2 / g to 5 m 2 / g, can secure the space around the negative electrode active material in the negative electrode, and minimizes the electrode deformation due to the volume expansion of the negative electrode active material, so there is an effect of improving the life of the electrode.

[0111] In addition, the generated lithium silicate gel shrinks to coat the periphery of the negative electrode active material, and the lithium silicate gel coating layer can act as a resistor to prevent the elution of Li from the negative electrode active material.

[0112] In one embodiment of the present invention, the above-described content can be similarly applied to the negative electrode active material and the negative electrode active material layer included in the negative electrode.

[0113] In one embodiment of the present invention, the negative electrode active material may contain 4 to 12 parts by weight of Li based on 100 parts by weight of the negative electrode active material.

[0114] In one embodiment of the present invention, the negative electrode active material layer may further contain a carbon-based active material. Specifically, the weight ratio of the negative electrode active material to the carbon-based active material may be 30:70 to 5:95. More specifically, the weight ratio of the negative electrode active material to the carbon-based active material may be 20:80 to 10:90, 16:84 to 14:86, or 15:85.

[0115] The negative electrode according to the above-described embodiment shows a lower pH than the conventional negative electrode, shows a high BET specific surface area, and can show remarkable improvements in charge-discharge capacity, initial efficiency, and life.

[0116] The negative electrode according to one embodiment of the present invention includes a current collector and a negative electrode active material layer disposed on the current collector. The negative electrode active material layer includes the above-described negative electrode active material and a conductive material.

[0117] The negative electrode active material layer may further contain the above-described thickener and binder.

[0118] The secondary battery according to one embodiment of the present invention may include the negative electrode according to the above-described one embodiment. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, and the negative electrode is the same as the above-described negative electrode. Since the negative electrode has been described above, a specific description thereof will be omitted.

[0119] The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and containing the positive electrode active material.

[0120] In the positive electrode, the positive electrode current collector is not particularly limited as long as it has conductivity without inducing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or those obtained by surface treatment of the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. can be used. Further, the positive electrode current collector may usually have a thickness of 3 to 500 μm, and fine irregularities can also be formed on the surface of the current collector to enhance the adhesive force of the positive electrode active material. For example, it may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven fabrics, etc.

[0121] The positive electrode active material can be a commonly used positive electrode active material. Specifically, the positive electrode active material is a layered compound such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; lithium iron oxide such as LiFe3O4; the chemical formula Li 1+c1 Mn 2-c1 O4 (0 ≦ c1 ≦ 0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7; the chemical formula LiNi 1-c2 Mc2O2 (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and satisfies 0.01 ≦ c2 ≦ 0.5); Ni-site type lithium nickel oxide represented by; the chemical formula LiMn 2-c3 M c3 O2 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01 ≦ c3 ≦ 0.1) or lithium manganese composite oxide represented by Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); or, for example, LiMn2O4 in which a part of the chemical formula of Li is substituted with an alkaline earth metal ion, etc., but is not limited only to these. The positive electrode may be Li-metal.

[0122] The positive electrode active material layer may contain a positive electrode conductive material and a positive electrode binder together with the above-described positive electrode active material.

[0123] At this time, the positive electrode conductive material is used to impart conductivity to the electrode, and in the battery to be configured, it can be used without particular limitation as long as it has electronic conductivity without causing a chemical change. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based substances such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. Among these, one kind alone or a mixture of two or more kinds may be used.

[0124] In addition, the positive electrode binder serves to improve the adhesion between the positive electrode active material particles and the adhesive force between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof. Among these, one kind alone or a mixture of two or more kinds may be used.

[0125] As the separation membrane, it separates the negative electrode and the positive electrode and provides a migration path for lithium ions. Usually, any material can be used without particular limitation as long as it is used as a separation membrane in a secondary battery. In particular, a material with low resistance to the migration of electrolyte ions and excellent electrolyte moisture retention ability is preferred. Specifically, a porous polymer film, for example, a porous polymer film made from polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof may be used. Also, a normal porous non-woven fabric, for example, a non-woven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may be used. Further, in order to ensure heat resistance or mechanical strength, a coated separation membrane containing a ceramic component or a polymer substance can also be used, and it may be selectively used in a single-layer or multi-layer structure.

[0126] Examples of the electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0127] Specifically, the electrolyte may contain a non-aqueous organic solvent and a metal salt.

[0128] Examples of the non-aqueous organic solvent include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl pyruvate, ethyl propionate, etc. may be used.

[0129] In particular, ethylene carbonate and propylene carbonate, which are cyclic carbonates among the carbonate-based organic solvents, are high-viscosity organic solvents and have a high dielectric constant, which can dissociate lithium salts well, so they can be preferably used. When such cyclic carbonates are mixed with linear carbonates having low viscosity and low dielectric constant, such as dimethyl carbonate and diethyl carbonate, at an appropriate ratio, an electrolyte having high electrical conductivity can be produced and can be more preferably used.

[0130] The metal salt can be a lithium salt, and the lithium salt is a substance that is easily dissolved in the non-aqueous electrolyte. For example, as the anion of the lithium salt, F - , Cl - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3- 、(CF3SO2)2N - 、(FSO2)2N - 、CF3CF2(CF3)2CO - 、(CF3SO2)2CH - 、(SF5)3C - 、(CF3SO2)3C - 、CF3(CF2)7SO3 - 、CF3CO2 - 、CH3CO2 - 、SCN - and (CF3CF2SO2)2N - One or more selected from the group consisting of may be used.

[0131] In addition to the electrolyte components, the electrolyte may further contain one or more additives such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, triamide hexaline, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol or aluminum trichloride for the purpose of improving the life characteristics of the battery, suppressing the decrease in battery capacity, improving the discharge capacity of the battery, etc.

[0132] According to another embodiment of the present invention, there are provided a battery module including the secondary battery as a unit cell and a battery pack including the same. Since the battery module and the battery pack include the secondary battery having a high capacity, high rate characteristics and cycle characteristics, they can be used as a power source for medium to large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles and power storage systems.

Examples

[0133] Hereinafter, preferred embodiments are presented to assist in the understanding of the present invention. However, the said embodiments are merely for illustrative purposes of this description, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope of this description and the scope of the technical idea. It goes without saying that such modifications and amendments belong to the scope of the appended claims.

[0134] <Examples and Comparative Examples> [Example 1] 1) Production of negative electrode slurry As a silicon-based negative electrode active material, a SiOx (x = 1) active material containing 8 wt% Li (average particle size (D 50 ): 6 μm) and graphite as a carbon-based negative electrode active material (average particle size (D 50 ): 20 μm) were mixed at a weight ratio of 15:85 and used as the negative electrode material. The said negative electrode material, conductive material (Super C65), and thickening agent (carboxymethyl cellulose, CMC) were mixed at a weight ratio of 98:1:1, and this was added to distilled water, which is a solvent for forming the negative electrode slurry, to produce a preliminary negative electrode slurry.

[0135] The said preliminary negative electrode slurry and boric acid (H3BO 3、 pK a = 9.2 at 25 °C) were added and mixed at a weight ratio of 99.5:0.5.

[0136] Subsequently, the acid-added preliminary negative electrode slurry and a binder (styrene-butadiene rubber, SBR) were mixed at a weight ratio of 98:2 to produce a negative electrode slurry.

[0137] 2) Production of negative electrode The said negative electrode slurry was coated on one side of a copper current collector (thickness: 15 μm) as a current collector at a loading amount of 3.6 mAh / cm 2 , dried in a chamber at 100 °C for 5 minutes (first drying), and then rolled (Roll press) to produce a preliminary electrode with a packing density of 1.6 g / cc.

[0138] The preliminary electrode was dried at 130°C for 8 hours in a vacuum chamber (second drying) to produce the final electrode (negative electrode).

[0139] [Example 2] A negative electrode was produced in the same manner as in Example 1, except that phosphoric acid (H3PO4, pK a = 2.16 at 25°C) was used instead of boric acid.

[0140] [Example 3] A negative electrode was produced in the same manner as in Example 1, except that the mixing ratio of the preliminary negative electrode slurry and boric acid was changed to 99:1.

[0141] [Example 4] A negative electrode was fabricated in the same way as in Example 1, except that the preliminary electrode was dried at 100°C for 8 hours in a vacuum chamber.

[0142] [Comparative Example 1] A negative electrode was manufactured in the same manner as in Example 1, except that boric acid was not added to the preliminary negative electrode slurry.

[0143] [Comparative Example 2] A negative electrode was produced in the same manner as in Example 1, except that boric acid was not added to the preliminary negative electrode slurry and the rolling was carried out so that the packing density during rolling was 1.5 g / cc.

[0144] [Comparative Example 3] A negative electrode was manufactured in the same way as in Example 1, except that hydrochloric acid (HCl, pK a = -6.3 at 25°C) was used instead of boric acid.

[0145] The compositions of the negative electrode slurries and negative electrodes produced in the above Examples and Comparative Examples are as shown in Tables 1 and 2 below.

[0146] Also, after separating the negative electrode active material layer from the current collector in the negative electrodes manufactured in the above Examples and Comparative Examples, a dispersion was prepared by mixing 5 g of the negative electrode active material layer and 100 g of water, and the pH was measured and described in Table 2.

[0147]

Table 1

Table 2

[0148] The BET specific surface area of the negative electrode was measured by the BET six-point method by removing gas (degassing) at 130 °C for 5 hours and performing N2 adsorption / desorption at 77 K using a BET measuring device (BEL-SORP-MAX, Nippon Bell).

[0149] <Experimental Example: Discharge Capacity, Initial Efficiency, Life (Capacity Retention Rate) Characteristic Evaluation> The negative electrodes manufactured in the Examples and Comparative Examples were used as the positive electrode with a lithium (Li) metal thin film cut into a circle of 1.7671 cm 2 . A lithium coin half-cell was manufactured by injecting an electrolytic solution in which vinylene carbonate dissolved at 0.5 parts by weight was dissolved in a mixed solution having a mixed volume ratio of methyl ethyl carbonate (EMC) and ethylene carbonate (EC) of 7:3 through a porous polyethylene separator between the positive electrode and the negative electrode.

[0150] Charge and discharge were performed on the manufactured battery, and the discharge capacity, initial efficiency, and capacity retention rate were evaluated and described in Table 3 below.

[0151] For the first and second cycles, charge and discharge were performed at 0.1 C, and from the third cycle, charge and discharge were performed at 0.5 C. The 300th cycle ended in a charged state (with lithium contained in the negative electrode).

[0152] Charging conditions: CC (constant current) / CV (constant voltage) (5 mV / 0.005C current cut-off)

[0153] Discharging conditions: CC (constant current) condition 1.5V

[0154] Through the results of one charge-discharge cycle, the discharge capacity (mAh / g) and the initial efficiency (%) were derived. Specifically, the initial efficiency (%) was derived by the following calculation.

[0155] Initial efficiency (%) = (Discharge capacity after one discharge / Charge capacity for one charge) × 100

[0156] The capacity retention rate and the electrode thickness change rate were derived by the following calculations, respectively.

[0157] Capacity retention rate (%) = (Discharge capacity after 299 discharges / Discharge capacity after one discharge) × 100

[0158]

Table 3

[0159] The manufacturing method according to the present invention includes a process of adding an acid during the manufacture of the negative electrode slurry, and from the lithium silicate gel thus formed, a negative electrode with a high porosity and a high specific surface area and a low pH of the negative electrode dispersion can be manufactured.

[0160] In Tables 1 to 3 above, in Examples 1 to 4, even when silicon-based particles containing Li compounds were used, the negative electrode slurry and the negative electrode showed a lower pH than before, the porosity increased around the negative electrode active material and the specific surface area became higher, the space around the negative electrode active material in the negative electrode could be secured, and the electrode deformation due to the volume expansion of the negative electrode active material was minimized. Therefore, it can be confirmed that all of the discharge capacity, the initial efficiency, and the capacity retention rate are excellent.

[0161] On the other hand, in Comparative Examples 1 and 2, since an acid was not added during the production of the negative electrode, no lithium silicate gel was formed, the voids in the electrode did not develop, and as a result, the pH of the negative electrode dispersion was high and the specific surface area of the negative electrode was low. During charge and discharge, it was confirmed that the volume expansion / contraction of the electrode was intense and the capacity retention rate of the battery decreased significantly.

[0162] In Comparative Example 3, it was confirmed that the pH of the negative electrode slurry was too low and excessive gelation occurred, resulting in an excessively high specific surface area of the negative electrode. As a result, it was confirmed that the capacity retention rate of the battery decreased significantly.

Claims

1. Preparing a preliminary negative electrode slurry containing a negative electrode active material and a conductive material, the negative electrode active material containing silicon-based particles containing an Li compound; Adding an acid to the preliminary negative electrode slurry and mixing to form a negative electrode slurry; Coating the negative electrode slurry on at least one surface of a current collector, and performing first drying and rolling to form a negative electrode active material layer; and Second drying the current collector on which the negative electrode active material layer is formed A method for manufacturing a negative electrode, comprising: The method for manufacturing a negative electrode, wherein the pH of the negative electrode slurry at 25°C is 10 or more and less than 12.

5.

2. The method for manufacturing a negative electrode according to claim 1, wherein the pH of the preliminary negative electrode slurry at 25°C is 12.5 or more and 13 or less.

3. The method for manufacturing a negative electrode according to claim 1, wherein the preliminary negative electrode slurry further contains a thickener.

4. The step of adding an acid to the preliminary negative electrode slurry and mixing to form a negative electrode slurry further includes the step of adding a binder and mixing after adding an acid to the preliminary negative electrode slurry and mixing, the method for manufacturing a negative electrode according to claim 1.

5. The acid is one or more selected from the group consisting of phosphoric acid, acetic acid, citric acid, oxalic acid, and boric acid, the method for manufacturing a negative electrode according to claim 1.

6. The pK of the acid at 25°C ａ is 1.5 to 13, the method for manufacturing a negative electrode according to claim 1.

7. The acid is added in an amount of 0.01 to 1.5 parts by weight based on 100 parts by weight in total of the preliminary negative electrode slurry, the method for manufacturing a negative electrode according to claim 1.

8. The viscosity of the negative electrode slurry at 25°C is 6,000 cP to 20,000 cP, and the method for manufacturing a negative electrode according to claim 1.

9. The negative electrode active material layer formed by the first drying and rolling contains a lithium silicate gel, and the method for manufacturing a negative electrode according to claim 1.

10. The BET specific surface area of the negative electrode after the second drying increases by 5% to 40% compared to the BET specific surface area of the negative electrode before the second drying, and the method for manufacturing a negative electrode according to claim 1.

11. A negative electrode including a current collector; and a negative electrode active material layer provided on the current collector, The negative electrode active material layer contains a negative electrode active material, The negative electrode active material contains silicon-based particles containing an Li compound, After separating the negative electrode active material layer from the current collector, the pH of a dispersion obtained by mixing 5 g of the negative electrode active material layer and 100 g of water is 10 or more and less than 12.5 at 25°C, and the negative electrode.

12. The packing density of the negative electrode is 1 g / cc to 2 g / cc, The BET specific surface area of the negative electrode is 2 m ２ / g to 5 m ２ / g, and the negative electrode according to claim 11.

13. The negative electrode active material contains 4 parts by weight to 12 parts by weight of Li based on 100 parts by weight of the negative electrode active material, The negative electrode active material layer further contains a carbon-based active material, The weight ratio of the negative electrode active material to the carbon-based active material is 30:70 to 5:95, and the negative electrode according to claim 11.

14. The negative electrode active material layer is coated with a loading amount of 3 mAh / cm ２ to 4 mAh / cm ２ , and the negative electrode according to claim 11.

15. A secondary battery including the negative electrode according to any one of claims 11 to 14.

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